The present invention relates to a refrigeration apparatus, and particularly relates to a refrigeration apparatus which has a refrigerant circuit configured to be capable of switching between a cooling operation and a heating operation and which performs a multistage compression refrigeration cycle.
As one conventional example of a refrigeration apparatus which has a refrigerant circuit configured to be capable of switching between a cooling operation and a heating operation and which performs a multistage compression refrigeration cycle, there is disclosed in Patent Document 1 an air-conditioning apparatus which has a refrigerant circuit configured to be capable of switching between an air-cooling operation and an air-warming operation and which performs a two-stage compression refrigeration cycle. This air-conditioning apparatus primarily has a compressor having two compression elements connected in series, a four-way switching valve for switching between an air-cooling operation and an air-warming operation, an outdoor heat exchanger, and an indoor heat exchanger.
<Patent Document 1>
Japanese Laid-open Patent Application No. 2007-232263
A refrigeration apparatus according to a first aspect of the present invention comprises a compression mechanism, a heat source-side heat exchanger which functions as a radiator or evaporator of refrigerant, a usage-side heat exchanger which functions as an evaporator or radiator of refrigerant, a switching mechanism, and an intermediate heat exchanger. The compression mechanism has a plurality of compression elements and is configured so that the refrigerant discharged from the first-stage compression element, which is one of a plurality of compression elements, is sequentially compressed by the second-stage compression element. As used herein, the term “compression mechanism” refers to a compressor in which a plurality of compression elements are integrally incorporated, or a configuration that includes a compressor in which a single compression element is incorporated and/or a plurality of compressor in which a plurality of compression elements have been incorporated are connected together. The phrase “the refrigerant discharged from a first-stage compression element, which is one of the plurality of compression elements, is sequentially compressed by a second-stage compression element” does not mean merely that two compression elements connected in series are included, namely, the “first-stage compression element” and the “second-stage compression element,” but that a plurality of compression elements are connected in series and the relationship between the compression elements is the same as the relationship between the aforementioned “first-stage compression element” and “second-stage compression element.” The switching mechanism is a mechanism for switching between a cooling operation state wherein refrigerant is circulated sequentially through the compression mechanism, the heat source-side heat exchanger functioning as a refrigerant radiator, and the usage-side heat exchanger functioning as an evaporator of refrigerant; and a heating operation state wherein refrigerant is circulated sequentially through the compression mechanism, the usage-side heat exchanger functioning as a refrigerant radiator, and the heat source-side heat exchanger functioning as an evaporator of refrigerant. The intermediate heat exchanger is a heat exchanger capable of functioning as a cooler of refrigerant discharged from the first-stage compression element and drawn into the second-stage compression element when the switching mechanism has been set to the cooling operation state, and also capable of functioning as an evaporator of refrigerant whose heat is radiated in the usage-side heat exchanger when the switching mechanism has been set to the heating operation state.
In a conventional air-conditioning apparatus, since the refrigerant discharged from a first stage compression element of the compressor is drawn into a second-stage compression element of the compressor and further compressed, the temperature of the refrigerant discharged from the second-stage compression element of the compressor increases. In an outdoor heat exchanger functioning as a refrigerant radiator, for example, the temperature difference between the refrigerant and the water and/or air as a heating source increases, and heat radiation loss in the outdoor heat exchanger increases, therefore causing a problem in that high operation efficiency is difficult to obtain.
As a countermeasure to this problem, in cases in which an intermediate heat exchanger is provided which functions as a cooler of refrigerant discharged from the first-stage compression element and drawn into the second-stage compression element, such as is the case with this refrigeration apparatus, the temperature of the refrigerant drawn into the second-stage compression element is lower, and the temperature of the refrigerant ultimately discharged from the compression mechanism can therefore be kept low in comparison with cases in which no intermediate heat exchanger is provided. Operation efficiency can therefore be improved during the cooling operation because heat radiation loss during the cooling operation can be reduced in the heat source-side heat exchanger which functions as a refrigerant radiator.
However, since an intermediate heat exchanger is provided, the heat that would have been useable in the usage-side heat exchanger during the heating operation if there were no intermediate heat exchanger functioning as a cooler of refrigerant discharged from the first-stage compression element and drawn into the second-stage compression element during the heating operation is radiated to the exterior from the intermediate heat exchanger, whereby the heating capacity in the usage-side heat exchanger decreases, and the operation efficiency during the heating operation decreases.
As a countermeasure to this, for example, an intermediate heat exchanger bypass tube for bypassing the intermediate heat exchanger is provided, and during the heating operation the intermediate heat exchanger bypass tube is used so that the refrigerant discharged from the first-stage compression element and drawn into the second-stage compression element bypasses the intermediate heat exchanger so as not to be cooled, thereby creating a state in which the intermediate heat exchanger is not used, whereby the loss of heating capacity in the usage-side heat exchanger is minimized during the heating operation, and operation efficiency during the heating operation can be prevented from decreasing.
However, when a state is created in which the intermediate heat exchanger is not used during the heating operation, the intermediate heat exchanger is provided as a heat exchanger used only during the cooling operation, and the intermediate heat exchanger will therefore be a device not used during the heating operation.
In view of this, in this refrigeration apparatus, the intermediate heat exchanger is made to function as a cooler when the switching mechanism has been set to the cooling operation state, and when the switching mechanism has been set to the heating operation state, the intermediate heat exchanger is made to function as an evaporator of refrigerant whose heat is radiated in the usage-side heat exchanger. Therefore, in this refrigeration apparatus, the temperature of the refrigerant discharged from the compression mechanism can be minimized during the cooling operation, and during the heating operation, the refrigerant evaporation capacity can be improved while the heat radiated to the exterior from the intermediate heat exchanger can be minimized.
Thereby, in this refrigeration apparatus, during the cooling operation, heat radiation loss in the heat source-side heat exchanger functioning as a refrigerant radiator is reduced, and the operation efficiency during the cooling operation can be improved, while during the heating operation, it is possible to efficiently use the intermediate heat exchanger, loss of heating capacity in the usage-side heat exchanger can be minimized, and the operation efficiency during the heating operation can be prevented from decreasing.
The refrigeration apparatus according to a second aspect of the present invention is the refrigeration apparatus according to the first aspect, wherein the intermediate heat exchanger is provided with an intermediate refrigerant tube for drawing the refrigerant discharged from the first-stage compression element into the second-stage compression element, an intermediate heat exchanger bypass tube is connected to the intermediate refrigerant tube so as to bypass the intermediate heat exchanger; and the refrigeration apparatus further comprises an intake return tube for connecting one end of the intermediate heat exchanger with an intake side of the compression mechanism, and an intermediate heat exchanger return tube for connecting the other end of the intermediate heat exchanger with the portion between the usage-side heat exchanger and the heat source-side heat exchanger.
In this refrigeration apparatus, the intermediate-pressure refrigerant flowing through the intermediate refrigerant tube can be cooled by the intermediate heat exchanger during the cooling operation, and during the heating operation, the intermediate-pressure refrigerant flowing through the intermediate refrigerant tube is made to bypass the intermediate heat exchanger by the intermediate heat exchanger bypass tube, and some of the refrigerant cooled in the usage-side heat exchanger can be drawn into and evaporated in the intermediate heat exchanger and can be returned to the intake side of the compression mechanism by the intake return tube and the intermediate heat exchanger return tube.
The refrigeration apparatus according to a third aspect of the present invention is the refrigeration apparatus according to the second aspect, wherein at the start of the operation for setting the switching mechanism to the cooling operation state, the refrigerant discharged from the first-stage compression element is drawn into the second-stage compression element through the intermediate heat exchanger bypass tube, and the intermediate heat exchanger is connected with the intake side of the compression mechanism through the intake return tube.
In this refrigeration apparatus, at the start of the operation for setting the switching mechanism to the cooling operation state, since the refrigerant discharged from the first-stage compression element is drawn into the second-stage compression element through the intermediate heat exchanger bypass tube and the intermediate heat exchanger is connected with the intake side of the compression mechanism through the intake return tube, even if liquid refrigerant accumulates in the intermediate heat exchanger at the start of the operation for setting the switching mechanism to the cooling operation state, this liquid refrigerant can be removed from the intermediate heat exchanger. Thereby, at the start of the operation for setting the switching mechanism to the cooling operation state, it is possible to avoid states in which liquid refrigerant has accumulated in the intermediate heat exchanger, and the refrigerant discharged from the first-stage compression element can be drawn into the second-stage compression element through the intermediate heat exchanger without any liquid compression occurring in the second-stage compression element as a result of liquid refrigerant accumulating in the intermediate heat exchanger.
The refrigeration apparatus according to a fourth aspect of the present invention is the refrigeration apparatus according to the second or third aspect, wherein the intermediate heat exchanger return tube is provided with a flow rate control valve.
In this refrigeration apparatus, refrigerant can be prevented from flowing into the intermediate heat exchanger return tube during the cooling operation, and it is possible to achieve a reliable distribution between the flow rate of the refrigerant flowing through the heat source-side heat exchanger and the flow rate of the refrigerant flowing through the intermediate heat exchanger during the heating operation.
The refrigeration apparatus according to a fifth aspect of the present invention is the refrigeration apparatus according to any of the first through fourth aspects, wherein an expansion device for isentropically expanding the refrigerant flowing between the heat source-side heat exchanger and the usage-side heat exchanger is connected to the portion between the heat source-side heat exchanger and the usage-side heat exchanger via a rectifier circuit which rectifies the refrigerant flow so that refrigerant flows in from the inlet of the expansion device both in cases in which refrigerant flows from the heat source-side heat exchanger to the usage-side heat exchanger and cases in which refrigerant flows from the usage-side heat exchanger to the heat source-side heat exchanger.
In this refrigeration apparatus, it is possible to improve the coefficient of performance and to recover energy through the expansion device during both the cooling operation and the heating operation, and operation efficiency during both the cooling operation and the heating operation can therefore be further improved.
The refrigeration apparatus according to a sixth aspect of the present invention is the refrigeration apparatus according to the fifth aspect, wherein a gas-liquid separator for performing gas-liquid separation of the refrigerant is connected to an outlet of the expansion device, and a second-stage injection tube for returning to the second-stage compression element gas refrigerant separated in the gas-liquid separator is connected to the gas-liquid separator.
In this refrigeration apparatus, operation efficiency can be further improved because intermediate pressure injection can be performed for returning intermediate-pressure refrigerant to the second-stage compression element.
Embodiments of the refrigeration apparatus according to the present invention are described hereinbelow with reference to the drawings.
(1) Configuration of Air-Conditioning Apparatus
The refrigerant circuit 10 of the air-conditioning apparatus 1 primarily has a compression mechanism 2, a switching mechanism 3, a heat source-side heat exchanger 4, a bridge circuit 17, a receiver 18, a first expansion mechanism 5a, a second expansion mechanism 5b, a usage-side heat exchanger 6, and an intermediate heat exchanger 7.
In the present embodiment, the compression mechanism 2 is configured from a compressor 21 which uses two compression elements to subject a refrigerant to two-stage compression. The compressor 21 has a hermetic structure in which a compressor drive motor 21b, a drive shaft 21c, and compression elements 2c, 2d are housed within a casing 21a. The compressor drive motor 21b is linked to the drive shaft 21c. The drive shaft 21c is linked to the two compression elements 2c, 2d. Specifically, the compressor 21 has a so-called single-shaft two-stage compression structure in which the two compression elements 2c, 2d are linked to a single drive shaft 21c and the two compression elements 2c, 2d are both rotatably driven by the compressor drive motor 21b. In the present embodiment, the compression elements 2c, 2d are rotary elements, scroll elements, or another type of positive displacement compression element. The compressor 21 is configured so as to admit refrigerant through an intake tube 2a, to discharge this refrigerant to an intermediate refrigerant tube 8 after the refrigerant has been compressed by the compression element 2c, to draw the refrigerant discharged to the intermediate refrigerant tube 8 into the compression element 2d, and to discharge the refrigerant to a discharge tube 2b after the refrigerant has been further compressed. The intermediate refrigerant tube 8 is a refrigerant tube for drawing refrigerant into the compression element 2d connected to the second-stage side of the compression element 2c after the refrigerant has been discharged at an intermediate pressure in the refrigeration cycle from the compression element 2c connected to the first-stage side of the compression element 2d. The discharge tube 2b is a refrigerant tube for feeding refrigerant discharged from the compression mechanism 2 to the switching mechanism 3, and the discharge tube 2b is provided with an oil separation mechanism 41 and a non-return mechanism 42. The oil separation mechanism 41 is a mechanism for separating refrigerator oil accompanying the refrigerant from the refrigerant discharged from the compression mechanism 2 and returning the oil to the intake side of the compression mechanism 2, and the oil separation mechanism 41 has primarily an oil separator 41a for separating refrigerator oil accompanying the refrigerant from the refrigerant discharged from the compression mechanism 2, and an oil return tube 41b connected to the oil separator 41a for returning the refrigerator oil separated from the refrigerant to the intake tube 2a of the compression mechanism 2. The oil return tube 41b is provided with a pressure-reducing mechanism 41c for depressurizing the refrigerator oil flowing through the oil return tube 41b. A capillary tube is used for the pressure-reducing mechanism 41c in the present embodiment. The non-return mechanism 42 is a mechanism for allowing the flow of refrigerant from the discharge side of the compression mechanism 2 to the heat source-side heat exchanger 4 as a radiator and for blocking the flow of refrigerant from the heat source-side heat exchanger 4 as a radiator to the discharge side of the compression mechanism 2, and a non-return valve is used in the present embodiment.
Thus, in the present embodiment, the compression mechanism 2 has two compression elements 2c, 2d and is configured so that among these compression elements 2c, 2d, refrigerant discharged from the first-stage compression element is compressed in sequence by the second-stage compression element.
The switching mechanism 3 is a mechanism for switching the direction of refrigerant flow in the refrigerant circuit 10. In order to allow the heat source-side heat exchanger 4 to function as a refrigerant radiator compressed by the compression mechanism 2 and to allow the usage-side heat exchanger 6 to function as an evaporator of refrigerant cooled in the heat source-side heat exchanger 4 during the air-cooling operation, the switching mechanism 3 is capable of connecting the discharge side of the compression mechanism 2 and one end of the heat source-side heat exchanger 4 and also connecting the intake side of the compressor 21 and the usage-side heat exchanger 6 (refer to the solid lines of the switching mechanism 3 in
Thus, focusing solely on the compression mechanism 2, the heat source-side heat exchanger 4, and the usage-side heat exchanger 6 constituting the refrigerant circuit 10; the switching mechanism 3 is configured so as to be capable of switching between the cooling operation state in which refrigerant is circulated in sequence through the compression mechanism 2, the heat source-side heat exchanger 4 functioning as a radiator of the refrigerant, and the usage-side heat exchanger 6 functioning as an evaporator of the refrigerant; and the heating operation state in which refrigerant is circulated in sequence through the compression mechanism 2, the usage-side heat exchanger 6 functioning as a radiator of the refrigerant, and the heat source-side heat exchanger 4 functioning as an evaporator of the refrigerant.
The heat source-side heat exchanger 4 is a heat exchanger that functions as a radiator or an evaporator of refrigerant. One end of the heat source-side heat exchanger 4 is connected to the switching mechanism 3, and the other end is connected to the first expansion mechanism 5a via the bridge circuit 17. Though not shown in the drawings, the heat source-side heat exchanger 4 is supplied with water or air as a cooling source for conducting heat exchange with the refrigerant flowing through the heat source-side heat exchanger 4.
The bridge circuit 17 is disposed between the heat source-side heat exchanger 4 and the usage-side heat exchanger 6, and is connected to a receiver inlet tube 18a connected to the inlet of the receiver 18 and to a receiver outlet tube 18b connected to the outlet of the receiver 18. The bridge circuit 17 has four non-return valves 17a, 17b, 17c, 17d in the present embodiment. The inlet non-return valve 17a is a non-return valve that allows only the flow of refrigerant from the heat source-side heat exchanger 4 to the receiver inlet tube 18a. The inlet non-return valve 17b is a non-return valve that allows only the flow of refrigerant from the usage-side heat exchanger 6 to the receiver inlet tube 18a. In other words, the inlet non-return valves 17a, 17b have a function for allowing refrigerant to flow from one among the heat source-side heat exchanger 4 and the usage-side heat exchanger 6 to the receiver inlet tube 18a. The outlet non-return valve 17c is a non-return valve that allows only the flow of refrigerant from the receiver outlet tube 18b to the usage-side heat exchanger 6. The outlet non-return valve 17d is a non-return valve that allows only the flow of refrigerant from the receiver outlet tube 18b to the heat source-side heat exchanger 4. In other words, the outlet non-return valves 17c, 17d have a function for allowing refrigerant to flow from the receiver outlet tube 18b to the heat source-side heat exchanger 4 or the usage-side heat exchanger 6.
The first expansion mechanism 5a is a mechanism for depressurizing the refrigerant, is provided to the receiver inlet tube 18a, and is an electrically driven expansion valve in the present embodiment. In the present embodiment, the first expansion mechanism 5a depressurizes the high-pressure refrigerant cooled in the heat source-side heat exchanger 4 to a nearly saturated pressure before feeding the refrigerant to the usage-side heat exchanger 6 via the receiver 18 during the air-cooling operation, and depressurizes the high-pressure refrigerant cooled in the usage-side heat exchanger 6 to a nearly saturated pressure before feeding the refrigerant to the heat source-side heat exchanger 4 via the receiver 18 during the air-warming operation.
The receiver 18 is a container provided in order to temporarily accumulate refrigerant that has been depressurized by the first expansion mechanism 5a, so that it is possible to collect excess refrigerant which may be produced depending on operation states in which the quantity of refrigerant circulated in the refrigerant circuit 10 differs between the air-cooling operation and the air-warming operation, for example. The inlet of the receiver 18 is connected to the receiver inlet tube 18a and the outlet is connected to the receiver outlet tube 18b. Also connected to the receiver 18 is a first intake return tube 18f capable of withdrawing refrigerant from inside the receiver 18 and returning the refrigerant to the intake tube 2a of the compression mechanism 2 (i.e., to the intake side of the compression element 2c on the first-stage side of the compression mechanism 2). This first intake return tube 18f is provided with a first intake return on/off valve 18g. The first intake return on/off valve 18g is an electromagnetic valve in the present embodiment.
The second expansion mechanism 5b is a mechanism provided to the receiver outlet tube 18b and used for depressurizing the refrigerant, and is an electrically driven expansion valve in the present embodiment. In the present embodiment, in the second expansion mechanism 5b, the refrigerant depressurized by the first expansion mechanism 5a is further depressurized during the air-cooling operation to a low pressure in the refrigeration cycle prior to being fed to the usage-side heat exchanger 6 via the receiver 18, and the refrigerant depressurized by the first expansion mechanism 5a is further depressurized during the air-warming operation to a low pressure in the refrigeration cycle prior to being sent to the heat source-side heat exchanger 4 via the receiver 18.
The usage-side heat exchanger 6 is a heat exchanger that functions as an evaporator or refrigerant radiator. One end of the usage-side heat exchanger 6 is connected to the first expansion mechanism 5a via the bridge circuit, and the other end is connected to the switching mechanism 3. Though not shown in the drawings, the usage-side heat exchanger 6 is supplied with water or air as a heating source for conducting heat exchange with the refrigerant flowing through the usage-side heat exchanger 6.
Thus, in the present embodiment, when the switching mechanism 3 is brought to the cooling operation state by the bridge circuit 17, the receiver 18, the receiver inlet tube 18a, and the receiver outlet tube 18b, the high-pressure refrigerant cooled in the heat source-side heat exchanger 4 can be fed to the usage-side heat exchanger 6 through the inlet non-return valve 17a of the bridge circuit 17, the first expansion mechanism 5a of the receiver inlet tube 18a, the receiver 18, the second expansion mechanism 5b of the receiver outlet tube 18b, and the outlet non-return valve 17c of the bridge circuit 17. When the switching mechanism 3 is brought to the heating operation state, the high-pressure refrigerant cooled in the usage-side heat exchanger 6 can be fed to the heat source-side heat exchanger 4 through the inlet non-return valve 17b of the bridge circuit 17, the first expansion mechanism 5a of the receiver inlet tube 18a, the receiver 18, the second expansion mechanism 5b of the receiver outlet tube 18b, and the outlet non-return valve 17d of the bridge circuit 17.
The intermediate heat exchanger 7 is provided to the intermediate refrigerant tube 8, and is either a cooler of the refrigerant discharged from the first-stage compression element 2c and drawn into the compression element 2d, or a heat exchanger capable of functioning as an evaporator of the refrigerant whose heat has been radiated in the usage-side heat exchanger 6. Though not shown in the drawings, the intermediate heat exchanger 7 is supplied with water or air as a cooling source for conducting heat exchange with the refrigerant flowing through the intermediate heat exchanger 7. Thus, it is acceptable to say that the intermediate heat exchanger 7 is a cooler that uses an external heating source, meaning that the intermediate heat exchanger does not use the refrigerant that circulates through the refrigerant circuit 10.
An intermediate heat exchanger bypass tube 9 is connected to the intermediate refrigerant tube 8 so as to bypass the intermediate heat exchanger 7. This intermediate heat exchanger bypass tube 9 is a refrigerant tube for limiting the flow rate of refrigerant flowing through the intermediate heat exchanger 7. The intermediate heat exchanger bypass tube 9 is provided with an intermediate heat exchanger bypass on/off valve 11. The intermediate heat exchanger bypass on/off valve 11 is an electromagnetic valve in the present embodiment. Excluding cases in which temporary operations such as the hereinafter-described air-cooling start control are performed, in the present embodiment the intermediate heat exchanger bypass on/off valve 11 is essentially controlled so as to close when the switching mechanism 3 is set for the cooling operation state, and to open when the switching mechanism 3 is set for the heating operation state. In other words, the intermediate heat exchanger bypass on/off valve 11 is closed when the air-cooling operation is performed and opened when the air-warming operation is performed.
In the intermediate refrigerant tube 8, an intermediate heat exchanger on/off valve 12 is provided to the portion extending from the connection with the end of the intermediate heat exchanger bypass tube 9 near the first-stage compression element 2c to the end of the intermediate heat exchanger 7 near the first-stage compression element 2c. This intermediate heat exchanger on/off valve 12 is a mechanism for limiting the flow rate of refrigerant flowing through the intermediate heat exchanger 7. The intermediate heat exchanger on/off valve 12 is an electromagnetic valve in the present embodiment. Excluding cases in which temporary operations such as the hereinafter-described air-cooling start control are performed, in the present embodiment the intermediate heat exchanger on/off valve 12 is essentially controlled so as to open when the switching mechanism 3 is set for the cooling operation state, and to close when the switching mechanism 3 is set for the heating operation state. In other words, the intermediate heat exchanger on/off valve 12 is controlled so as to open when the air-cooling operation is performed and close when the air-warming operation is performed.
The intermediate refrigerant tube 8 is also provided with a non-return mechanism 15 for allowing refrigerant to flow from the discharge side of the first-stage compression element 2c to the intake side of the second-stage compression element 2d and for blocking the refrigerant from flowing from the intake side of the second-stage compression element 2d to the discharge side of the first-stage compression element 2c. The non-return mechanism 15 is a non-return valve in the present embodiment. In the present embodiment, the non-return mechanism 15 is provided to the intermediate refrigerant tube 8 in the portion extending from the end of the intermediate heat exchanger 7 near the second-stage compression element 2d to the connection with the end of the intermediate heat exchanger bypass tube 9 near the second-stage compression element 2d.
Furthermore, a second intake return tube 92 is connected to one end of the intermediate heat exchanger 7 (here, the end near the first-stage compression element 2c), and an intermediate heat exchanger return tube 94 is connected to the other end of the intermediate heat exchanger 7 (herein, the end near the second-stage compression element 2d). This second intake return tube 92 is a refrigerant tube for connecting one end of the intermediate heat exchanger 7 and the intake side of the compressor 2 (here, the intake tube 2a) during a state in which the refrigerant discharged from the first-stage compression element 2c is being drawn into the second-stage compression element 2d through the intermediate heat exchanger bypass tube 9. The intermediate heat exchanger return tube 94 is a refrigerant tube for connecting the portion between the usage-side heat exchanger 6 and the heat source-side heat exchanger 4 (here, the portion between the second expansion mechanism 5b which depressurizes the refrigerant to a low pressure in the refrigeration cycle and the heat source-side heat exchanger 4 as an evaporator) with the other end of the intermediate heat exchanger 7, when the refrigerant discharged from the first-stage compression element 2c is being drawn into the second-stage compression element 2d through the intermediate heat exchanger bypass tube 9 and the switching mechanism 3 has been set to the heating operation state. In the present embodiment, the second intake return tube 92 is connected at one end to the portion of the intermediate refrigerant tube 8 extending from the connection with the end of the intermediate heat exchanger bypass tube 9 near the first-stage compression element 2c to the end of the intermediate heat exchanger 7 near the first-stage compression element 2c, while the other end is connected to the intake side of the compressor 2 (here, the intake tube 2a). One end of the intermediate heat exchanger return tube 94 is connected to the portion extending from the second expansion mechanism 5b to the heat source-side heat exchanger 4, while the other end is connected to the portion of the intermediate refrigerant tube 8 extending from the end of the intermediate heat exchanger 7 near the first-stage compression element 2c to the non-return mechanism 15. The second intake return tube 92 is also provided with a second intake return on/off valve 92a, and the intermediate heat exchanger return tube 94 is provided with an intermediate heat exchanger return on/off valve 94a. The second intake return on/off valve 92a and the intermediate heat exchanger return on/off valve 94a are electromagnetic valves in the present embodiment. Excluding cases in which temporary operations such as the hereinafter-described air-cooling start control are performed, in the present embodiment the second intake return on/off valve 92a is essentially controlled so as to close when the switching mechanism 3 is set for the cooling operation state, and to open when the switching mechanism 3 is set for the heating operation state. The intermediate heat exchanger return on/off valve 94a is controlled so as to close when the switching mechanism 3 is set for the cooling operation state and to open when the switching mechanism 3 is set for the heating operation state, including cases in which temporary operations such as the hereinafter-described air-cooling start control are performed.
Thus, in the present embodiment, owing primarily to the intermediate heat exchanger bypass tube 9, the second intake return tube 92, and the intermediate heat exchanger return tube 94, the intermediate-pressure refrigerant flowing through the intermediate refrigerant tube 8 can be cooled by the intermediate heat exchanger 7 during the air-cooling operation; and during the air-warming operation, the intermediate-pressure refrigerant flowing through the intermediate refrigerant tube 8 can be made to bypass the intermediate heat exchanger 7 by the intermediate heat exchanger bypass tube 9, and some of the refrigerant cooled in the usage-side heat exchanger 6 can be drawn into and evaporated in the intermediate heat exchanger 7 and returned to the intake side of the compression mechanism 2 by the second intake return tube 92 and the intermediate heat exchanger return tube 94.
Furthermore, though not shown in the drawings, the air-conditioning apparatus 1 has a controller for controlling the actions of the components constituting the air-conditioning apparatus 1, including the compression mechanism 2, the switching mechanism 3, the expansion mechanisms 5a, 5b, the intermediate heat exchanger bypass on/off valve 11, the intermediate heat exchanger on/off valve 12, the first intake return on/off valve 18g, the second intake return on/off valve 92a, the intermediate heat exchanger return on/off valve 94a, and the like.
(2) Action of the Air-Conditioning Apparatus
Next, the action of the air-conditioning apparatus 1 of the present embodiment will be described using
<Air-Cooling Operation>
During the air-cooling operation, the switching mechanism 3 is brought to the cooling operation state shown by the solid lines in
When the refrigerant circuit 10 is in this state, low-pressure refrigerant (refer to point A in
Thus, in the air-conditioning apparatus 1 of the present embodiment, the intermediate heat exchanger 7 is provided to the intermediate refrigerant tube 8 for drawing refrigerant discharged from the compression element 2c into the compression element 2d, and in the air-cooling operation the intermediate heat exchanger on/off valve 12 is opened and the intermediate heat exchanger bypass on/off valve 11 of the intermediate heat exchanger bypass tube 9 is closed, thereby putting the intermediate heat exchanger 7 into a state of functioning as a cooler. Therefore, the refrigerant drawn into the compression element 2d on the second-stage side of the compression element 2c decreases in temperature (refer to points B1 and C1 in
<Air-Warming Operation>
During the air-warming operation, the switching mechanism 3 is brought to the heating operation state shown by the dashed lines in
When the refrigerant circuit 10 is in this state, low-pressure refrigerant (refer to point A in
Thus, in the air-conditioning apparatus 1 of the present embodiment, during the air-warming operation in which the switching mechanism 3 is set to the heating operation state, the intermediate heat exchanger on/off valve 12 is closed and the intermediate heat exchanger bypass on/off valve 11 is opened, thereby putting the intermediate heat exchanger 7 into a state of not functioning as a cooler. Therefore, the temperature decrease is minimized in the refrigerant discharged from the compression mechanism 2 (refer to points D and D′ in
Moreover, in the air-conditioning apparatus 1 of the present embodiment, during the air-warming operation in which the switching mechanism 3 is set for the heating operation state, the intermediate heat exchanger 7 is not merely set to a state of not functioning as a cooler due to not being used. Instead, the intermediate heat exchanger 7, along with the heat source-side heat exchanger 4, is made to function as an evaporator of the refrigerant whose heat has been radiated in the usage-side heat exchanger 6, and is used during the air-warming operation as well to increase refrigerant-evaporating capacity during the air-warming operation and to increase the quantity of refrigerant circulating within the refrigerant circuit 10 while minimizing the heat radiated from the intermediate heat exchanger 7 to the exterior, for example, thereby minimizing the decrease in heating capacity in the usage-side heat exchanger 6. Thereby, in the air-conditioning apparatus 1 of the present embodiment, heat radiation loss decreases in the heat source-side heat exchanger 4 functioning as a refrigerant radiator during the air-cooling operation, and operating efficiency during the air-cooling operation can be improved. During the air-warming operation, it is possible to use the intermediate heat exchanger 7 more effectively, minimize the reduction in the heating capacity of the heat source-side heat exchanger 6, and prevent operating efficiency during the air-warming operation from decreasing.
<Air-Cooling Start Control>
With the intermediate heat exchanger 7 described above, there is a risk of liquid refrigerant accumulating when the air-conditioning apparatus 1 has stopped, or in other instances. When the above-described air-cooling operation is started during a state in which liquid refrigerant has accumulated in the intermediate heat exchanger 7, the liquid refrigerant accumulated in the intermediate heat exchanger 7 is drawn into the second-stage compression element 2d; therefore, the liquid begins to be compressed in the second-stage compression element 2d, and the reliability of the compression mechanism 2 is compromised.
In view whereof, in the present embodiment, during the start of the above-described air-cooling operation, a state is created in which the refrigerant discharged from the first-stage compression element 2c is drawn into the second-stage compression element 2d through the intermediate heat exchanger bypass tube 9, and air-cooling start control is performed in which the intermediate heat exchanger 7 and the intake side of the compression mechanism 2 are connected by the second intake return tube 92.
The air-cooling start control of the present embodiment is described in detail hereinbelow using
First, in step S1, when a command to start the air-cooling operation is issued, the process advances to operating the various valves in step S2.
Next, in step S2, the on/off state of the on/off valves 11, 12, 92a is switched to a refrigerant return state in which the refrigerant discharged from the first-stage compression element 2c through the intermediate heat exchanger bypass tube 9 is drawn into the second-stage compression element 2d, and the intermediate heat exchanger 7 and the intake side of the compression mechanism 2 are connected through the second intake return tube 92. Specifically, the intermediate heat exchanger bypass on/off valve 11 is opened and the intermediate heat exchanger on/off valve 12 is closed. A flow is thus created by the intermediate heat exchanger bypass tube 9 in which the refrigerant discharged from the first-stage compression element 2c is drawn into the second-stage compression element 2d without passing through the intermediate heat exchanger 7. In other words, the intermediate heat exchanger 7 is put into a state of not functioning as a cooler, and a state is created in which the refrigerant discharged from the first-stage compression element 2c is drawn into the second-stage compression element 2d through the intermediate heat exchanger bypass tube 9 (see
Next, in step S3, the on/off state of the on/off valves 11, 12, 92a in step S2 (i.e., the refrigerant return state) is maintained for a predetermined time duration. Thereby, even if liquid refrigerant has accumulated in the intermediate heat exchanger 7 while the air-conditioning apparatus 1 has been stopped, for example, the liquid refrigerant accumulated inside the intermediate heat exchanger 7 is depressurized and evaporated, then removed out of the intermediate heat exchanger 7 (more specifically, to the intake side of the compression mechanism 2) without being drawn into the second-stage compression element 2d, and is drawn into the compression mechanism 2 (the first-stage compression element 2c, in this case). The predetermined time duration is herein set to a time duration whereby the liquid refrigerant accumulating in the intermediate heat exchanger 7 can be drawn out of the intermediate heat exchanger 7.
Next, in step S4, the on/off state of the on/off valves 11, 12, 92a is switched to a refrigerant non-return state in which the refrigerant discharged from the first-stage compression element 2c is drawn into the second-stage compression element 2d through the intermediate heat exchanger 7, and the intermediate heat exchanger 7 and the intake side of the compression mechanism 2 are not connected through the second intake return tube 92. In other words, a transition is made to the on/off state of the valves 11, 12, 92a during the above-described air-cooling operation, and the air-cooling start control is ended. Specifically, the second intake return on/off valve 92a is closed. A state is thus created in which the refrigerant inside the intermediate heat exchanger 7 does not flow out to the intake side of the compression mechanism 2. In this type of state, the intermediate heat exchanger on/off valve 12 is then opened, and the intermediate heat exchanger bypass on/off valve 11 is closed. A state is thus created in which the intermediate heat exchanger 7 functions as a cooler.
Thereby, in the air-conditioning apparatus 1, during the start of the air-cooling operation, there is no liquid compression in the second-stage compression element 2d, which would occur as a result of liquid refrigerant accumulating in the intermediate heat exchanger 7, and the reliability of the compression mechanism 2 can be improved.
(3) Modification 1
In the embodiment described above, switching between the air-cooling operation and air-cooling start control, i.e., switching between the refrigerant non-return state and the refrigerant return state was performed by changing the on/off state of the on/off valves 11, 12, 92a, but another option is a refrigerant circuit 110 as shown in
The intermediate heat exchanger switching valve 93 herein is a valve capable of switching between the refrigerant non-return state and the refrigerant return state, and in the present modification is a four-way switching valve connected to the discharge side of the first-stage compression element 2c of the intermediate refrigerant tube 8, the inlet side of the intermediate heat exchanger 7 of the intermediate refrigerant tube 8, the end of the intermediate heat exchanger bypass tube 9 on the side near the first-stage compression element 2c, and the end of the second intake return tube 92 on the side near the intermediate heat exchanger 7. The intermediate heat exchanger bypass tube 9 is also provided with a non-return mechanism 9a for allowing refrigerant to flow from the discharge side of the first-stage compression element 2c to the intake side of the second-stage compression element 2d and for blocking the refrigerant from flowing from the intake side of the second-stage compression element 2d to the discharge side of the first-stage compression element 2c and the intake side of the compression mechanism 2. The non-return mechanism 9a is a non-return valve in the present modification.
In the present modification, although a detailed description is not given, the same air-cooling operation as in the embodiment described above can be performed by switching the intermediate heat exchanger switching valve 93 to the refrigerant non-return state (refer to the solid lines of the intermediate heat exchanger switching valve 93 in
The same operational effects as those of the embodiment described above can also be achieved with the configuration of the present modification. Moreover, in the present modification, since the refrigerant non-return state and the refrigerant return state can be switched by the intermediate heat exchanger switching valve 93, the number of valves can be reduced in comparison with the case of using the configuration in which the refrigerant non-return state and the refrigerant return state are switched by a plurality of valves 11, 12, 92a such as those of the embodiment described above. Since pressure loss is reduced in comparison with cases of using electromagnetic valves, the decrease in intermediate pressure in the refrigeration cycle can be minimized, and the decrease operating efficiency can also be minimized.
(4) Modification 2
In the above-described embodiment and the modification thereof, consideration is given to using a configuration in which the intermediate heat exchanger 7 and the heat source-side heat exchanger 4 are heat exchangers that use air as a heat source (that is, as a cooling source or a heating source), and air as a heat source is supplied by a common heat source-side fan 40 (described hereinafter) to both heat exchangers 4, 7.
For example, in cases in which the air-conditioning apparatus 1 has a configuration in which a heat source unit 1a provided primarily with the heat source-side fan 40, the heat source-side heat exchanger 4, and the intermediate heat exchanger 7 is connected with a usage unit (not shown) provided primarily with the usage-side heat exchanger 6, the heat source unit 1a such as is shown in
The heat source unit 1a constituting the air-conditioning apparatus 1 of the present modification is a so-called upward-blowing type in which air is drawn in from the sides and the air is blown upwards, the heat source unit 1a having primarily a casing 71, and disposed inside the casing 71 a heat source-side heat exchanger 4, a intermediate heat exchanger 7, and other refrigerant circuit structural components, and/or a heat source-side fan 40 and other devices.
In the present modification, the casing 71 is a substantially rectangular parallelepiped-shaped box, and is configured primarily from a top plate 72 constituting the top surface of the casing 71, a left plate 73 constituting the external peripheral surface of the casing 71, a right plate 74, a front plate 75, a rear plate 76, and a bottom plate 77. The top plate 72 is primarily a member constituting the top surface of the casing 71, and in the present modification is a plate-shaped member seen as a substantial rectangle in a plan view, an air-blowing opening 71a being formed substantially in the middle. A fan grill 78 is provided to the top plate 72 so as to cover the air-blowing opening 71a from above. The left plate 73 is primarily a member constituting the left surface of the casing 71, and in the present modification is plate-shaped member seen as a substantial rectangle in a side view, extending downward from the left edge of the top plate 72. Intake openings 73a are formed throughout almost the entire left plate 73, except for the top part. The right plate 74 is primarily a member constituting the right surface of the casing 71, and in the present modification is a plate-shaped member seen as a substantial rectangle in a side view, extending downward from the right edge of the top plate 72. Intake openings 74a are formed throughout almost the entire right plate 74, except for the top part. The front plate 75 is a member primarily constituting the front surface of the casing 71, and in the present modification is configured from a plate-shaped member seen as a substantial rectangle in a front view, disposed in sequence below the front edge of the top plate 72. The rear plate 76 is primarily a member constituting the rear surface of the casing 71, and in the present modification is configured from a plate-shaped member seen as a substantial rectangle in a front view, disposed in sequence below the rear edge of the top plate 72. Intake openings 76a are formed throughout almost the entire rear plate 76, except for the top part. The bottom plate 77 is primarily a member constituting the bottom surface of the casing 71, and in the present modification is a plate-shaped member seen as a substantial rectangle in a plan view.
In the present modification, the intermediate heat exchanger 7 is integrated with the heat source-side heat exchanger 4 in a state of being disposed above the heat source-side heat exchanger 4, and is also disposed on top of the bottom plate 77. More specifically, the intermediate heat exchanger 7 is integrated with the heat source-side heat exchanger 4 due to sharing heat transfer fins. The integration of the heat source-side heat exchanger 4 and the intermediate heat exchanger 7 forms a heat exchanger panel seen as a substantial U shape in a plan view in the present modification, and this panel is disposed so as to face the intake openings 73a, 74a, 76a. The heat source-side fan 40 is directed towards the air-blowing opening 71a of the top plate 72, and is disposed on the top side of the integration of the heat source-side heat exchanger 4 and the intermediate heat exchanger 7 (i.e., the heat exchanger panel). In the present modification, the heat source-side fan 40 is an axial flow fan and is rotatably driven by a fan drive motor 40a, whereby air as a heat source is drawn from the intake openings 73a, 74a, 76a into the casing 71, and after passing through the heat source-side heat exchanger 4 and the intermediate heat exchanger 7, the air can be blown upwards from the air-blowing opening 71a (refer to the arrows indicating the flow of air in
The intermediate heat exchanger 7 and the heat source-side heat exchanger 4 are integrated and the intermediate heat exchanger 7 is disposed in the top part of the heat exchanger panel consisting of the two integrated heat exchangers in light of the fact that the air-conditioning apparatus 1 of the present modification uses a refrigerant that operates in a supercritical range (carbon dioxide in this case), and also the fact that the heat source unit 1a is a model that draws air in from the sides and blows the air upward. To describe these facts in detail, sometimes the refrigeration cycle of the air-cooling operation, for example, is performed (see
In this type of heat source unit 1a, if the intermediate heat exchanger bypass tube 9 were to be used during the air-warming operation so that the refrigerant discharged from the first-stage compression element 2c and drawn into the second-stage compression element 2d bypasses the intermediate heat exchanger 7 so as not to be cooled therein and the intermediate heat exchanger 7 is not used, there would be a severe disadvantage in that the intermediate heat exchanger 7, which is disposed in a position where the flow rate of air as a heat source is fastest in light of the heat transfer coefficient during the air-cooling operation, would not contribute at all during the air-warming operation, and the intermediate heat exchanger 7 would not be effectively used.
However, during the air-warming operation in the present modification, as in the above-described embodiment and the modification thereof, the intermediate heat exchanger bypass tube 9 is used so that the refrigerant discharged from the first-stage compression element 2c and drawn into the second-stage compression element 2d bypasses the intermediate heat exchanger 7 so as not to be cooled therein, and the intermediate heat exchanger 7 is made to function as an evaporator of refrigerant, thereby contributing to improving the evaporation capacity during the air-warming operation.
(5) Modification 3
In the above-described embodiment and the modifications thereof, the air-conditioning apparatus 1 which is configured to be capable of switching between the air-cooling operation and the air-warming operation via the switching mechanism 3 and which performs a two-stage compression refrigeration cycle is provided with an intermediate heat exchanger 7 that functions as a cooler of the refrigerant discharged from the first-stage compression element 2c and drawn into the second-stage compression element 2d, an intermediate heat exchanger bypass tube 9 connected to the intermediate refrigerant tube 8 so as to bypass the intermediate heat exchanger 7, a second intake return tube 92 for connecting one end of the intermediate heat exchanger 7 and the intake side of the compression mechanism 2, and an intermediate heat exchanger return tube 94 for connecting the portion between the usage-side heat exchanger 6 and the heat source-side heat exchanger 4 with the other end of the intermediate heat exchanger 7, but in addition to this configuration, intermediate pressure injection may be performed by a first second-stage injection tube 19 and an economizer heat exchanger 20.
For example, the refrigerant circuit 10 (see
The first second-stage injection tube 19 has a function for branching off and returning the refrigerant flowing between the heat source-side heat exchanger 4 and the usage-side heat exchanger 6 to the second-stage compression element 2d of the compression mechanism 2. In the present modification, the first second-stage injection tube 19 is provided so as to branch off refrigerant flowing through the receiver inlet tube 18a and return the refrigerant to the second-stage compression element 2d. More specifically, the first second-stage injection tube 19 is provided so as to branch off refrigerant from a position upstream of the first expansion mechanism 5a of the receiver inlet tube 18a (i.e., a position between the heat source-side heat exchanger 4 and the first expansion mechanism 5a when the switching mechanism 3 is set to the cooling operation state) and return the refrigerant to a position in the intermediate refrigerant tube 8 downstream of the intermediate heat exchanger 7. The first second-stage injection tube 19 is provided with a first second-stage injection valve 19a whose opening degree can be controlled. The first second-stage injection valve 19a is an electrically driven expansion valve in the present modification.
The economizer heat exchanger 20 is a heat exchanger for carrying out heat exchange between the refrigerant flowing between the heat source-side heat exchanger 4 and the usage-side heat exchanger 6 and the refrigerant that flows through the first second stage injection tube 19 (more specifically, the refrigerant that has been depressurized to a nearly intermediate pressure in the first second-stage injection valve 19a). In the present modification, the economizer heat exchanger 20 is provided so as to perform heat exchange between the refrigerant flowing through a position in the receiver inlet tube 18a upstream of the first expansion mechanism 5a (i.e., between the heat source-side heat exchanger 4 and the first expansion mechanism 5a when the switching mechanism 3 is set to the cooling operation state) and the refrigerant flowing through the first second-stage injection tube 19, and the economizer heat exchanger 20 has a flow passage through which both refrigerants flow against each other. In the present modification, the economizer heat exchanger 20 is provided farther downstream than the position where the first second-stage injection tube 19 branches from the receiver inlet tube 18a. Therefore, the refrigerant flowing between the heat source-side heat exchanger 4 and the usage-side heat exchanger 6 is branched off in the receiver inlet tube 18a into the first second-stage injection tube 19 before undergoing heat exchange in the economizer heat exchanger 20, and heat exchange is then conducted in the economizer heat exchanger 20 with the refrigerant flowing through the first second-stage injection tube 19.
Thus, in the present modification, when the switching mechanism 3 is set to the cooling operation state, the high-pressure refrigerant cooled in the heat source-side heat exchanger 4 can be fed to the usage-side heat exchanger 6 through the inlet non-return valve 17a of the bridge circuit 17, the economizer heat exchanger 20, the first expansion mechanism 5a of the receiver inlet tube 18a, the receiver 18, the second expansion mechanism 5b of the receiver outlet tube 18b, and the outlet non-return valve 17c of the bridge circuit 17. When the switching mechanism 3 is brought to the heating operation state, the high-pressure refrigerant cooled in the usage-side heat exchanger 6 can be fed to the heat source-side heat exchanger 4 through the inlet non-return valve 17b of the bridge circuit 17, the economizer heat exchanger 20, the first expansion mechanism 5a of the receiver inlet tube 18a, the receiver 18, the second expansion mechanism 5b of the receiver outlet tube 18b, and the outlet non-return valve 17d of the bridge circuit 17.
Furthermore, in the present modification, the intermediate refrigerant tube 8 or the compression mechanism 2 is provided with an intermediate pressure sensor 54 for detecting the pressure of the refrigerant that flows through the intermediate refrigerant tube 8. The outlet of the first second-stage injection tube 19 side of the economizer heat exchanger 20 is provided with an economizer outlet temperature sensor 55 for detecting the temperature of the refrigerant at the outlet of the first second-stage injection tube 19 side of the economizer heat exchanger 20.
Next, the action of the air-conditioning apparatus 1 of the present modification will be described using
<Air-Cooling Operation>
During the air-cooling operation, the switching mechanism 3 is brought to the cooling operation state shown by the solid lines in
When the refrigerant circuit 210 is in this state, low-pressure refrigerant (refer to point A in
In the configuration of the present modification, as in Modification 2 described above, since the intermediate heat exchanger 7 is in a state of functioning as a cooler during the air-cooling operation in which the switching mechanism 3 is brought to the cooling operation state, heat radiation loss in the heat source-side heat exchanger 4 can be reduced in comparison with cases in which no intermediate heat exchanger 7 is provided.
Moreover, in the configuration of the present modification, since the first second-stage injection tube 19 and the economizer heat exchanger 20 are provided so as to branch off refrigerant fed from the heat source-side heat exchanger 4 to the expansion mechanisms 5a, 5b and return the refrigerant to the second-stage compression element 2d, the temperature of refrigerant drawn into the second-stage compression element 2d can be kept even lower (refer to points C1 and G in
In the present modification, as in Modification 2 described above, at the start of the air-cooling operation in which the switching mechanism 3 is set to the cooling operation state, the refrigerant discharged from the first-stage compression element 2c is drawn into the second-stage compression element 2d through the intermediate heat exchanger bypass tube 9, and the intermediate heat exchanger 7 and the intake side of the compression mechanism 2 are connected through the second intake return tube 92. Therefore, even if liquid refrigerant has accumulated in the intermediate heat exchanger 7 prior to the start of the operation in which the switching mechanism 3 is set to the cooling operation state, the liquid refrigerant can be removed from the intermediate heat exchanger 7. Thereby, at the start of the operation in which the switching mechanism 3 is set to the cooling operation state, it is possible to avoid a state of liquid refrigerant accumulating inside the intermediate heat exchanger 7, liquid compression does not occur in the second-stage compression element 2d as a result of liquid refrigerant accumulating in the intermediate heat exchanger 7, and the reliability of the compression mechanism 2 can be improved.
<Air-Warming Operation>
During the air-warming operation, the switching mechanism 3 is brought to the heating operation state shown by the dashed lines in
When the refrigerant circuit 210 is in this state, low-pressure refrigerant (refer to point A in
In the configuration of the present modification, as in Modification 2 described above, during the air-warming operation in which the switching mechanism 3 is set to the heating operation state, heat radiation to the exterior can be minimized, the decrease of heating capacity can be minimized, and decreases in operating efficiency can be prevented in comparison with cases in which only the intermediate heat exchanger 7 is provided and/or cases in which the intermediate heat exchanger 7 is made to function as a cooler, similar to the air-cooling operation described above.
Moreover, in the configuration of the present modification, since the first second-stage injection tube 19 and the economizer heat exchanger 20 are provided so as to branch off refrigerant fed from the heat source-side heat exchanger 4 to the expansion mechanisms 5a, 5b and return the refrigerant to the second-stage compression element 2d in the same manner as the air-cooling operation, the temperature of refrigerant drawn into the second-stage compression element 2d can be kept even lower (refer to points B1 and G in
In the configuration of the present modification, similar to the embodiment described above, during the air-cooling operation, there is less heat radiation loss in the heat source-side heat exchanger 4 functioning as a refrigerant radiator, and the operating efficiency during the air-cooling operation can be improved. During the air-warming operation, it is possible to effectively use the intermediate heat exchanger 7, minimize the loss of heating capacity in the usage-side heat exchanger 6, and prevent the operating efficiency during the air-warming operation from decreasing.
Advantages of both the air-cooling operation and the air-warming operation in the configuration of the present modification are that the economizer heat exchanger 20 is a heat exchanger which has flow channels through which refrigerant fed from the heat source-side heat exchanger 4 or usage-side heat exchanger 6 to the expansion mechanisms 5a, 5b and refrigerant flowing through the second-stage injection tube 19 both flow so as to oppose each other; therefore, it is possible to reduce the temperature difference between the refrigerant fed to the expansion mechanisms 5a, 5b from the heat source-side heat exchanger 4 or the usage-side heat exchanger 6 in the economizer heat exchanger 20 and the refrigerant flowing through the second-stage injection tube 19, and high heat exchange efficiency can be obtained.
In the present modification, switching between the air-cooling operation and the air-cooling start control, i.e., switching between the refrigerant non-return state and the refrigerant return state is performed through the on/off states of the on/off valves 11, 12, 92a, but another option instead of the on/off valves 11, 12, 92a is to provide an intermediate heat exchanger switching valve 93 capable of switching between the refrigerant non-return state and the refrigerant return state, as in Modification 1 described above.
Furthermore, particularly advantageous effects can be obtained when using the configuration of the heat source unit 1a, such as the one in Modification 2.
(6) Modification 4
In the refrigerant circuit 210 (see
However, in order to create a configuration having a plurality of usage-side heat exchangers 6 connected in parallel to each other, and to make it possible to control the flow rate of refrigerant flowing through the usage-side heat exchangers 6 and obtain the refrigeration load required by the usage-side heat exchangers 6, the objective being to perform air-cooling or air-warming corresponding to the air-conditioning loads of a plurality of air-conditioned spaces, for example; in some cases usage-side expansion mechanisms 5c are provided between the receiver 18 as a gas-liquid separator and the usage-side heat exchangers 6 so as to correspond to the usage-side heat exchangers 6.
For example, although the details are not shown, one possibility in the refrigerant circuit 210 (see
In this type of configuration as well, the intermediate pressure injection by the economizer heat exchanger 20 is advantageous similar to Modification 3 described above, under the condition that the pressure difference between the high pressure in the refrigeration cycle and the nearly intermediate pressure of the refrigeration cycle can be used without performing a severe depressurizing operation everywhere but the first expansion mechanism 5a as a heat source-side expansion mechanism after cooling takes place in the heat source-side heat exchanger 4 as a radiator, as is the case in the air-cooling operation in which the switching mechanism 3 is set to the cooling operation state.
However, in conditions such as those of the air-warming operation for setting the switching mechanism 3 to the heating operation state, the usage-side expansion mechanisms 5c control the flow rate of refrigerant flowing through the usage-side heat exchangers 6 as radiators so as to obtain the refrigeration loads required by the usage-side heat exchangers 6 as radiators, and the flow rate of refrigerant passing through the usage-side heat exchangers 6 as radiators is established for the most part by the operation of depressurizing the refrigerant by controlling the opening degrees of the usage-side expansion mechanisms 5c provided downstream of the usage-side heat exchangers 6 as radiators and upstream of the economizer heat exchanger 20. Under such conditions, the extent of refrigerant depressurization by controlling the opening degrees of the usage-side expansion mechanisms 5c fluctuates not only due to the flow rate of refrigerant flowing through the usage-side heat exchangers 6 as radiators, but also due to the state of flow rate distribution among the plurality of usage-side heat exchangers 6 as radiators, and there are cases in which the extent of depressurization differs greatly among the plurality of usage-side expansion mechanisms 5c, or the extent of depressurization in the usage-side expansion mechanisms 5c is comparatively large. Therefore, there is a risk of a decrease in the refrigerant pressure in the inlet of the economizer heat exchanger 20, and in such cases there is a risk that the quantity of heat exchanged in the economizer heat exchanger 20 (i.e., the flow rate of refrigerant flowing through the first second-stage injection tube 19) will decrease and usage will be difficult. Particularly in cases in which this type of air-conditioning apparatus 1 is configured as a separate-type air-conditioning apparatus in which a heat source unit including primarily a compression mechanism 2, a heat source-side heat exchanger 4, and a receiver 18 is connected by communication pipe with a usage unit including primarily a usage-side heat exchanger 6, the communication pipe might be extremely long depending on the arrangement of the usage unit and the heat source unit; therefore, in addition to the effects of pressure drop, the pressure of the refrigerant in the inlet of the economizer heat exchanger 20 further decreases. In cases in which there is a risk of a decrease in the pressure of the refrigerant in the inlet of the economizer heat exchanger 20, if the gas-liquid separator pressure is lower than the critical pressure, intermediate pressure injection by a useable gas-liquid separator is still advantageous even under conditions in which there is a small difference in pressure between the gas-liquid separator pressure and the intermediate pressure in the refrigeration cycle (here, the pressure of the refrigerant flowing through the intermediate refrigerant tube 8).
In view of this, in the present modification as shown in
The second second-stage injection tube 18c is a refrigerant tube capable of performing intermediate pressure injection for removing refrigerant from the receiver 18 and returning the refrigerant to the second-stage compression element 2d of the compression mechanism 2, and in the present modification, the second second-stage injection tube 18c is provided so as to connect the top part of the receiver 18 and the intermediate refrigerant tube 8 (i.e., the intake side of the second-stage compression element 2d of the compression mechanism 2). The second second-stage injection tube 18c is provided with a second second-stage injection on/off valve 18d and a second second-stage injection non-return mechanism 18e. The second second-stage injection on/off valve 18d is a valve capable of opening and closing, and is an electromagnetic valve in the present modification. The second second-stage injection non-return mechanism 18e is a mechanism for allowing refrigerant to flow from the receiver 18 to the second-stage compression element 2d and blocking refrigerant from flowing from the second-stage compression element 2d to the receiver 18, and a non-return valve is used in the present modification. The second second-stage injection tube 18c and the first intake return tube 18f are integrated in a portion near the receiver 18. The second second-stage injection tube 18c and the first second-stage injection tube 19 are integrated in a portion near the intermediate refrigerant tube 8. In the present modification, the usage-side expansion mechanisms 5c are electrically driven expansion valves. In the present modification, as described above, the first second-stage injection tube 19 and the economizer heat exchanger 20 are used during the air-cooling operation, and the second second-stage injection tube 18c is used during the air-warming operation; therefore, since there is no need for the direction of refrigerant flow to the economizer heat exchanger 20 to be constant for both the air-cooling operation and the air-warming operation, the bridge circuit 17 is omitted and the configuration of the refrigerant circuit 310 is simplified.
Next, the action of the air-conditioning apparatus 1 of the present modification will be described using
<Air-Cooling Operation>
During the air-cooling operation, the switching mechanism 3 is brought to the cooling operation state shown by the solid lines in
When the refrigerant circuit 310 is in this state, low-pressure refrigerant (refer to point A in
<Air-Warming Operation>
During the air-warming operation, the switching mechanism 3 is brought to the heating operation state shown by the dashed lines in
When the refrigerant circuit 310 is in this state, low-pressure refrigerant (refer to point A in
The configuration of the present modification is different from that of Modification 3 in that intermediate pressure injection is performed by the receiver 18 as a gas-liquid separator instead of intermediate pressure injection by the economizer heat exchanger 20 during the air-warming operation, but otherwise the same operational effects as those of Modification 3 can be obtained.
In the present modification, the switching between the air-cooling operation and air-cooling start control, i.e., the switching between the refrigerant non-return state and the refrigerant return state is performed by the on/off states of the on/off valves 11, 12, 92a, but an intermediate heat exchanger switching valve 93 capable of switching between the refrigerant non-return state and the refrigerant return state may be provided instead of the on/off valves 11, 12, 92a, as in Modification 1 described above.
Furthermore, particularly advantageous effects can be obtained when using the configuration of the heat source unit 1a such as the one in Modification 2.
(7) Modification 5
The refrigerant circuit 310 (see
In view of this, in the present modification, the refrigerant circuit 310 in Modification 4 described above is replaced by a refrigerant circuit 410 provided with a subcooling heat exchanger 96 and a third intake return tube 95 between the receiver 18 and the usage-side expansion mechanisms 5c, as shown in
The subcooling heat exchanger 96 is a heat exchanger for cooling the refrigerant fed from the receiver 18 to the usage-side expansion mechanisms 5c. More specifically, during the air-cooling operation, the subcooling heat exchanger 96 is a heat exchanger for performing heat exchange with the refrigerant flowing through the third intake return tube 95, which branches off some of the refrigerant fed from the receiver 18 to the usage-side expansion mechanisms 5c and returns the refrigerant to the intake side of the compression mechanism 2 (i.e., to the intake tube 2a between the compression mechanism 2 and the usage-side heat exchangers 6 as evaporators), and the subcooling heat exchanger 96 has a flow passage through which both refrigerants flow against each other. The third intake return tube 95 herein is a refrigerant tube for branching off the refrigerant fed from the heat source-side heat exchanger 4 as a radiator to the usage-side expansion mechanisms 5c and returning the refrigerant to the intake side of the compression mechanism 2 (i.e., the intake tube 2a). The third intake return tube 95 is provided with a third intake return valve 95a whose opening degree can be controlled, and in the subcooling heat exchanger 96, heat exchange is performed between the refrigerant fed from the receiver 18 to the usage-side expansion mechanisms 5c and the refrigerant flowing through the third intake return tube 95 after having been depressurized to a nearly low pressure in the third intake return valve 95a. The intake return valve 95a is an electrically driven expansion valve in the present modification. An intake pressure sensor 60 for detecting the pressure of the refrigerant flowing through the intake side of the compression mechanism 2 is provided to either the intake tube 2a or the compression mechanism 2. The outlet of the subcooling heat exchanger 96 on the side near the third intake return tube 95 is provided with a subcooling heat exchange outlet temperature sensor 59 for detecting the temperature of the refrigerant in the outlet of the subcooling heat exchanger 96 on the side near the third intake return tube 95.
Next, the action of the air-conditioning apparatus 1 in the present modification will be described using
<Air-Cooling Operation>
During the air-cooling operation, the switching mechanism 3 is brought to the cooling operation state shown by the solid lines in
When the refrigerant circuit 410 is in this state, low-pressure refrigerant (refer to point A in
<Air-Warming Operation>
During the air-warming operation, the switching mechanism 3 is brought to the heating operation state shown by the dashed lines in
When the refrigerant circuit 410 is in this state, low-pressure refrigerant (refer to point A in
In the configuration of the present modification, the same operational effects as those of Modification 5 described above are achieved, and the risk of an imbalanced flow of refrigerant during distribution to the usage-side expansion mechanisms 5c can be reduced because the refrigerant fed from the receiver 18 to the usage-side expansion mechanisms 5c during the air-cooling operation (refer to point I in
In the present modification, the switching between the air-cooling operation and air-cooling start control, i.e., the switching between the refrigerant non-return state and the refrigerant return state is performed by the on/off states of the on/off valves 11, 12, 92a, but an intermediate heat exchanger switching valve 93 capable of switching between the refrigerant non-return state and the refrigerant return state may be provided instead of the on/off valves 11, 12, 92a, as in Modification 1 described above.
Furthermore, particularly advantageous effects can be obtained when using the configuration of the heat source unit 1a such as the one in Modification 2.
(8) Modification 6
In the above-described embodiment and the modifications thereof, a two-stage compression-type compression mechanism 2 is configured such that the refrigerant discharged from the first-stage compression element of two compression elements 2c, 2d is sequentially compressed in the second-stage compression element by one compressor 21 having a single-axis two-stage compression structure, but other options include using a compression mechanism having more stages than a two-stage compression system, such as a three-stage compression system or the like; or configuring a multistage compression mechanism connecting in series a plurality of compressors incorporated with a single compression element and/or compressors incorporated with a plurality of compression elements. In cases in which the capacity of the compression mechanism must be increased, such as cases in which numerous usage-side heat exchangers 6 are connected, for example, a parallel multistage compression-type compression mechanism may be used in which two or more multistage compression-type compression mechanisms are connected in parallel.
For example, the refrigerant circuit 410 in Modification 5 described above (see
In the present modification, the first compression mechanism 103 is configured using a compressor 29 for subjecting the refrigerant to two-stage compression through two compression elements 103c, 103d, and is connected to a first intake branch tube 103a which branches off from an intake header tube 102a of the compression mechanism 102, and also to a first discharge branch tube 103b whose flow merges with a discharge header tube 102b of the compression mechanism 102. In the present modification, the second compression mechanism 104 is configured using a compressor 30 for subjecting the refrigerant to two-stage compression through two compression elements 104c, 104d, and is connected to a second intake branch tube 104a which branches off from the intake header tube 102a of the compression mechanism 102, and also to a second discharge branch tube 104b whose flow merges with the discharge header tube 102b of the compression mechanism 102. Since the compressors 29, 30 have the same configuration as the compressor 21 in the embodiment and modifications thereof described above, symbols indicating components other than the compression elements 103c, 103d, 104c, 104d are replaced with symbols beginning with 29 or 30, and these components are not described here. The compressor 29 is configured so that refrigerant is drawn from the first intake branch tube 103a, the refrigerant thus drawn in is compressed by the compression element 103c and then discharged to a first inlet-side intermediate branch tube 81 that constitutes the intermediate refrigerant tube 8, the refrigerant discharged to the first inlet-side intermediate branch tube 81 is caused to be drawn into the compression element 103d by way of an intermediate header tube 82 and a first outlet-side intermediate branch tube 83 constituting the intermediate refrigerant tube 8, and the refrigerant is further compressed and then discharged to the first discharge branch tube 103b. The compressor 30 is configured so that refrigerant is drawn in through the second intake branch tube 104a, the drawn-in refrigerant is compressed by the compression element 104c and then discharged to a second inlet-side intermediate branch tube 84 constituting the intermediate refrigerant tube 8, the refrigerant discharged to the second inlet-side intermediate branch tube 84 is drawn into the compression element 104d via the intermediate header tube 82 and a second outlet-side intermediate branch tube 85 constituting the intermediate refrigerant tube 8, and the refrigerant is further compressed and then discharged to the second discharge branch tube 104b. In the present modification, the intermediate refrigerant tube 8 is a refrigerant tube for drawing in refrigerant discharged from the compression elements 103c, 104c connected to the first-stage sides of the compression elements 103d, 104d into the compression elements 103d, 104d connected to the second-stage sides of the compression elements 103c, 104c, and the intermediate refrigerant tube 8 primarily comprises the first inlet-side intermediate branch tube 81 connected to the discharge side of the first-stage compression element 103c of the first compression mechanism 103, the second inlet-side intermediate branch tube 84 connected to the discharge side of the first-stage compression element 104c of the second compression mechanism 104, the intermediate header tube 82 whose flow merges with both inlet-side intermediate branch tubes 81, 84, the first outlet-side intermediate branch tube 83 branching off from the intermediate header tube 82 and connected to the intake side of the second-stage compression element 103d of the first compression mechanism 103, and the second outlet-side intermediate branch tube 85 branching off from the intermediate header tube 82 and connected to the intake side of the second-stage compression element 104d of the second compression mechanism 104. The discharge header tube 102b is a refrigerant tube for feeding refrigerant discharged from the compression mechanism 102 to the switching mechanism 3. A first oil separation mechanism 141 and a first non-return mechanism 142 are provided to the first discharge branch tube 103b connected to the discharge header tube 102b. A second oil separation mechanism 143 and a second non-return mechanism 144 are provided to the second discharge branch tube 104b connected to the discharge header tube 102b. The first oil separation mechanism 141 is a mechanism whereby refrigeration oil that accompanies the refrigerant discharged from the first compression mechanism 103 is separated from the refrigerant and returned to the intake side of the compression mechanism 102. The first oil separation mechanism 141 mainly has a first oil separator 141a for separating from the refrigerant the refrigeration oil that accompanies the refrigerant discharged from the first compression mechanism 103, and a first oil return tube 141b that is connected to the first oil separator 141a and that is used for returning the refrigeration oil separated from the refrigerant to the intake side of the compression mechanism 102. The second oil separation mechanism 143 is a mechanism whereby refrigeration oil that accompanies the refrigerant discharged from the second compression mechanism 104 is separated from the refrigerant and returned to the intake side of the compression mechanism 102. The second oil separation mechanism 143 mainly has a second oil separator 143a for separating from the refrigerant the refrigeration oil that accompanies the refrigerant discharged from the second compression mechanism 104, and a second oil return tube 143b that is connected to the second oil separator 143a and that is used for returning the refrigeration oil separated from the refrigerant to the intake side of the compression mechanism 102. In the present modification, the first oil return tube 141b is connected to the second intake branch tube 104a, and the second oil return tube 143c is connected to the first intake branch tube 103a. Accordingly, a greater amount of refrigeration oil returns to the compression mechanism 103, 104 that has the lesser amount of refrigeration oil even when there is an imbalance between the amount of refrigeration oil that accompanies the refrigerant discharged from the first compression mechanism 103 and the amount of refrigeration oil that accompanies the refrigerant discharged from the second compression mechanism 104, which is due to the imbalance in the amount of refrigeration oil retained in the first compression mechanism 103 and the amount of refrigeration oil retained in the second compression mechanism 104. The imbalance between the amount of refrigeration oil retained in the first compression mechanism 103 and the amount of refrigeration oil retained in the second compression mechanism 104 is therefore resolved. In the present modification, the first intake branch tube 103a is configured so that the portion leading from the flow juncture with the second oil return tube 143b to the flow juncture with the intake header tube 102a slopes downward toward the flow juncture with the intake header tube 102a, while the second intake branch tube 104a is configured so that the portion leading from the flow juncture with the first oil return tube 141b to the flow juncture with the intake header tube 102a slopes downward toward the flow juncture with the intake header tube 102a. Therefore, even if either one of the compression mechanisms 103, 104 is stopped, refrigeration oil being returned from the oil return tube corresponding to the operating compression mechanism to the intake branch tube corresponding to the stopped compression mechanism is returned to the intake header tube 102a, and there will be little likelihood of a shortage of oil supplied to the operating compression mechanism. The oil return tubes 141b, 143b are provided with pressure-reducing mechanisms 141c, 143c for depressurizing the refrigeration oil that flows through the oil return tubes 141b, 143b. The non-return mechanisms 142, 144 are mechanisms for allowing refrigerant to flow from the discharge side of the compression mechanisms 103, 104 to the switching mechanism 3, and for blocking the flow of refrigerant from the switching mechanism 3 to the discharge side of the compression mechanisms 103, 104.
Thus, in the present modification, the compression mechanism 102 is configured by connecting two compression mechanisms in parallel; namely, the first compression mechanism 103 having two compression elements 103c, 103d and configured so that refrigerant discharged from the first-stage compression element of these compression elements 103c, 103d is sequentially compressed by the second-stage compression element, and the second compression mechanism 104 having two compression elements 104c, 104d and configured so that refrigerant discharged from the first-stage compression element of these compression elements 104c, 104d is sequentially compressed by the second-stage compression element.
In the present modification, the intermediate heat exchanger 7 is provided to the intermediate header tube 82 constituting the intermediate refrigerant tube 8, and the intermediate heat exchanger 7 is a heat exchanger for cooling the mixed flow of the refrigerant discharged from the first-stage compression element 103c of the first compression mechanism 103 and the refrigerant discharged from the first-stage compression element 104c of the second compression mechanism 104. Specifically, the intermediate heat exchanger 7 functions as a shared cooler for two compression mechanisms 103, 104. Accordingly, the circuit configuration is simplified around the compression mechanism 102 when the intermediate heat exchanger 7 is provided to the parallel-multistage-compression-type compression mechanism 102 in which a plurality of multistage-compression-type compression mechanisms 103, 104 are connected in parallel.
The first inlet-side intermediate branch tube 81 constituting the intermediate refrigerant tube 8 is provided with a non-return mechanism 81a for allowing the flow of refrigerant from the discharge side of the first-stage compression element 103c of the first compression mechanism 103 toward the intermediate header tube 82 and for blocking the flow of refrigerant from the intermediate header tube 82 toward the discharge side of the first-stage compression element 103c, while the second inlet-side intermediate branch tube 84 constituting the intermediate refrigerant tube 8 is provided with a non-return mechanism 84a for allowing the flow of refrigerant from the discharge side of the first-stage compression element 104c of the second compression mechanism 104 toward the intermediate header tube 82 and for blocking the flow of refrigerant from the intermediate header tube 82 toward the discharge side of the first-stage compression element 104c. In the present modification, non-return valves are used as the non-return mechanisms 81a, 84a. Therefore, even if either one of the compression mechanisms 103, 104 has stopped, there are no instances in which refrigerant discharged from the first-stage compression element of the operating compression mechanism passes through the intermediate refrigerant tube 8 and travels to the discharge side of the first-stage compression element of the stopped compression mechanism. Accordingly, there are no instances in which refrigerant discharged from the first-stage compression element of the operating compression mechanism passes through the interior of the first-stage compression element of the stopped compression mechanism and exits out through the intake side of the compression mechanism 102, which would cause the refrigeration oil of the stopped compression mechanism to flow out, and it is thus unlikely that there will be insufficient refrigeration oil for starting up the stopped compression mechanism. In the case that the compression mechanisms 103, 104 are operated in order of priority (for example, in the case of a compression mechanism in which priority is given to operating the first compression mechanism 103), the stopped compression mechanism described above will always be the second compression mechanism 104, and therefore in this case only the non-return mechanism 84a corresponding to the second compression mechanism 104 need be provided.
In cases of a compression mechanism which prioritizes operating the first compression mechanism 103 as described above, since a shared intermediate refrigerant tube 8 is provided for both compression mechanisms 103, 104, the refrigerant discharged from the first-stage compression element 103c corresponding to the operating first compression mechanism 103 passes through the second outlet-side intermediate branch tube 85 of the intermediate refrigerant tube 8 and travels to the intake side of the second-stage compression element 104d of the stopped second compression mechanism 104, whereby there is a danger that refrigerant discharged from the first-stage compression element 103c of the operating first compression mechanism 103 will pass through the interior of the second-stage compression element 104d of the stopped second compression mechanism 104 and exit out through the discharge side of the compression mechanism 102, causing the refrigeration oil of the stopped second compression mechanism 104 to flow out, resulting in insufficient refrigeration oil for starting up the stopped second compression mechanism 104. In view of this, an on/off valve 85a is provided to the second outlet-side intermediate branch tube 85 in the present modification, and when the second compression mechanism 104 has stopped, the flow of refrigerant through the second outlet-side intermediate branch tube 85 is blocked by the on/off valve 85a. The refrigerant discharged from the first-stage compression element 103c of the operating first compression mechanism 103 thereby no longer passes through the second outlet-side intermediate branch tube 85 of the intermediate refrigerant tube 8 and travels to the intake side of the second-stage compression element 104d of the stopped second compression mechanism 104; therefore, there are no longer any instances in which the refrigerant discharged from the first-stage compression element 103c of the operating first compression mechanism 103 passes through the interior of the second-stage compression element 104d of the stopped second compression mechanism 104 and exits out through the discharge side of the compression mechanism 102 which causes the refrigeration oil of the stopped second compression mechanism 104 to flow out, and it is thereby even more unlikely that there will be insufficient refrigeration oil for starting up the stopped second compression mechanism 104. An electromagnetic valve is used as the on/off valve 85a in the present modification.
In the case of a compression mechanism which prioritizes operating the first compression mechanism 103, the second compression mechanism 104 is started up in continuation from the starting up of the first compression mechanism 103, but at this time, since a shared intermediate refrigerant tube 8 is provided for both compression mechanisms 103, 104, the starting up takes place from a state in which the pressure in the discharge side of the first-stage compression element 103c of the second compression mechanism 104 and the pressure in the intake side of the second-stage compression element 103d are greater than the pressure in the intake side of the first-stage compression element 103c and the pressure in the discharge side of the second-stage compression element 103d, and it is difficult to start up the second compression mechanism 104 in a stable manner. In view of this, in the present modification, there is provided a startup bypass tube 86 for connecting the discharge side of the first-stage compression element 104c of the second compression mechanism 104 and the intake side of the second-stage compression element 104d, and an on/off valve 86a is provided to this startup bypass tube 86. In cases in which the second compression mechanism 104 has stopped, the flow of refrigerant through the startup bypass tube 86 is blocked by the on/off valve 86a and the flow of refrigerant through the second outlet-side intermediate branch tube 85 is blocked by the on/off valve 85a. When the second compression mechanism 104 is started up, a state in which refrigerant is allowed to flow through the startup bypass tube 86 can be restored via the on/off valve 86a, whereby the refrigerant discharged from the first-stage compression element 104c of the second compression mechanism 104 is drawn into the second-stage compression element 104d via the startup bypass tube 86 without being mixed with the refrigerant discharged from the first-stage compression element 104c of the first compression mechanism 103, a state of allowing refrigerant to flow through the second outlet-side intermediate branch tube 85 can be restored via the on/off valve 85a at point in time when the operating state of the compression mechanism 102 has been stabilized (e.g., a point in time when the intake pressure, discharge pressure, and intermediate pressure of the compression mechanism 102 have been stabilized), the flow of refrigerant through the startup bypass tube 86 can be blocked by the on/off valve 86a, and operation can transition to the normal air-cooling operation. In the present modification, one end of the startup bypass tube 86 is connected between the on/off valve 85a of the second outlet-side intermediate branch tube 85 and the intake side of the second-stage compression element 104d of the second compression mechanism 104, while the other end is connected between the discharge side of the first-stage compression element 104c of the second compression mechanism 104 and the non-return mechanism 84a of the second inlet-side intermediate branch tube 84, and when the second compression mechanism 104 is started up, the startup bypass tube 86 can be kept in a state of being substantially unaffected by the intermediate pressure portion of the first compression mechanism 103. An electromagnetic valve is used as the on/off valve 86a in the present modification.
The action of the air-conditioning apparatus 1 of the present modification during the air-cooling operation, the air-warming operation, and the like are essentially the same as the action in the above-described Modification 5 (
The same operational effects as those of Modification 5 described above can also be achieved with the configuration of the present modification.
In the present modification, the switching between the air-cooling operation and air-cooling start control, i.e., the switching between the refrigerant non-return state and the refrigerant return state is performed by the on/off states of the on/off valves 11, 12, 92a, but an intermediate heat exchanger switching valve 93 capable of switching between the refrigerant non-return state and the refrigerant return state may be provided instead of the on/off valves 11, 12, 92a, as in Modification 1 described above.
Furthermore, particularly advantageous effects can be obtained when using the configuration of the heat source unit 1a such as the one in Modification 2.
(9) Modification 7
In the above-described embodiment and the modifications thereof, either a two-stage compression-type compression mechanism 2 is configured such that the refrigerant discharged from the first-stage compression element is sequentially compressed in the second-stage compression element by one compressor 21 having a single-axis two-stage compression structure, or a two-stage compression-type compression mechanism 102 is configured such that two single-axis two-stage compression-type compressors 29, 30 are connected in parallel, whereby the refrigerant discharged from the first-stage compression element is sequentially compressed by the second-stage compression element; but another option is to configure a two-stage compression-type compression mechanism such that compressors 22, 23 having single-stage compression structures are connected in series, whereby the refrigerant discharged from the first-stage compression element is sequentially compressed by the second-stage compression element.
For example, the refrigerant circuit 110 in Modification 1 described above (see
In the present modification, the compression mechanism 202 is configured from a compressor 22 in which refrigerant is compressed by a compression element 202c as a first-stage compression element, and a compressor 23 in which refrigerant is compressed by a compression element 202d as a second-stage compression element. The compressor 22 has a hermetic structure in which a casing 22a houses a compressor drive motor 22b, a drive shaft 22c, and a compression element 202c. The compressor drive motor 22b is linked to the drive shaft 22c. The compressor 23 has a hermetic structure in which a casing 23a houses a compressor drive motor 23b, a drive shaft 23c, and a compression element 202d. The compressor drive motor 23b is linked to the drive shaft 23c. In the present modification, the compression elements 202c, 202d are rotary elements, scroll elements, or another type of positive displacement compression element. The compression mechanism 202 is configured so as to draw in refrigerant through an intake tube 2a, to discharge this refrigerant to an intermediate refrigerant tube 8 after the refrigerant has been compressed by the compression element 202c of the compressor 22, to admit the refrigerant discharged to the intermediate refrigerant tube 8 into the compression element 202d of the compressor 23, and to discharge the refrigerant to a discharge tube 2b after the refrigerant has been further compressed.
The action of the air-conditioning apparatus 1 of the present modification during the air-cooling operation, the air-warming operation, and the like are essentially the same as the action in the above-described Modification 1 (
The same operational effects as those of Modification 1 and the like described above can also be obtained with the configuration of the present modification.
(10) Modification 8
In the embodiment described above and the modifications thereof, the intermediate heat exchanger return tube 94 is provided with the intermediate heat exchanger return on/off valve 94a composed of an electromagnetic valve, and control is performed for closing the valve when the switching mechanism 3 is in the cooling operation state and opening the valve when the switching mechanism 3 is in the heating operation state, but instead of this intermediate heat exchanger return on/off valve 94a, another option is to provide a flow rate control valve so as to enable control of the quantity of refrigerant flowing through the intermediate heat exchanger 7 functioning as an evaporator of refrigerant during the air-warming operation.
For example, the refrigerant circuit 610 in Modification 7 described above (see
The configuration of the present modification is different from that of Modification 7 described above in that refrigerant flows in the refrigerant circuit 710 sequentially through the first expansion mechanism 5a, the receiver 18, and the second expansion mechanism 5b via the bridge circuit 17 during the air-cooling operation and refrigerant flows in the refrigerant circuit 710 sequentially through the second expansion mechanism 5b, the receiver 18, and the first expansion mechanism 5a via the bridge circuit 17 during the air-warming operation (in Modification 7, refrigerant flows in the refrigerant circuit 610 sequentially through the first expansion mechanism 5a, the receiver, and the second expansion mechanism 5b during both the air-cooling operation and the air-warming operation), but otherwise the same operational effects as those of Modification 7 described above can be obtained. Moreover, in the configuration of the present modification, since the intermediate heat exchanger return valve 94b as a flow rate control valve is provided to the intermediate heat exchanger return tube 94, not only can the flow of refrigerant into the intermediate heat exchanger return tube 94 be prevented during the air-cooling operation, but it is also possible to reliably distribute the flow rate of refrigerant flowing through the heat source-side heat exchanger 4 and the flow rate of refrigerant flowing through the intermediate heat exchanger 7 during the heating operation.
(11) Modification 9
In the configurations of the above-described embodiment and the modifications thereof, an expansion device for isentropically expanding the refrigerant flowing between the heat source-side heat exchanger 4 and the usage-side heat exchanger 6 may be provided between the heat source-side heat exchanger 4 and the usage-side heat exchanger 6.
For example, the refrigerant circuit 710 in Modification 8 described above (see
The same operational effects as those of Modification 8 and the like described above can also be obtained with the configuration of the present modification. Moreover, in the configuration of the present modification, during the air-cooling operation, refrigerant flows in the refrigerant circuit 810 sequentially through the first expansion mechanism 5a, the expansion device 97, the receiver 18, and the second expansion mechanism 5b via the bridge circuit 17 as a rectifier circuit, and during the air-warming operation, refrigerant flows in the refrigerant circuit 810 sequentially through the second expansion mechanism 5b, the receiver 18, and the first expansion mechanism 5a via the bridge circuit 17 as a rectifier circuit, whereby the refrigerant is isentropically depressurized by the expansion device 97 during the process in which the refrigerant is depressurized from a high pressure to a low pressure in the refrigeration cycle during both the air-cooling operation and the air-warming operation (in other words, during the air-cooling operation, using
(12) Modification 10
In the configuration of Modification 9 described above, the receiver 18 positioned in the outlet of the expansion device 97 may be made to function as a gas-liquid separator, a second-stage injection tube may be connected for returning the gas refrigerant separated from the liquid in the receiver 18 to the second-stage compression element 2d, and intermediate pressure injection may be performed by the receiver 18 as a gas-liquid separator during both the air-cooling operation and the air-warming operation.
For example, the refrigerant circuit 810 (see
The second second-stage injection tube 18c is a refrigerant tube capable of performing intermediate pressure injection for removing refrigerant out of the receiver 18 and returning the refrigerant to the second-stage compression element 202d of the compression mechanism 202, and in the present modification, the second second-stage injection tube 18c is provided so as to connect the top part of the receiver 18 with the intermediate refrigerant tube 8 (i.e., with the intake side of the second-stage compression element 202d of the compression mechanism 202). The second second-stage injection on/off valve 18d and the second second-stage injection non-return mechanism 18e are provided to the second second-stage injection tube 18c. The second second-stage injection on/off valve 18d is a valve capable of opening and closing, and is an electromagnetic valve in the present modification. The second second-stage injection non-return mechanism 18e is a mechanism for allowing the flow of refrigerant from the receiver 18 to the second-stage compression element 202d and for blocking the flow of refrigerant from the second-stage compression element 202d to the receiver 18, and a non-return valve is used in the present modification. The second second-stage injection tube 18c and the first intake return tube 18f are integrated in the portion near the receiver 18.
The same operational effects as those of Modification 9 described above can also be obtained with the configuration of the present modification. Moreover, in the configuration of the present modification, operation efficiency can be further improved because it is also possible, during both the air-cooling operation and the air-warming operation, to cause the receiver 18 connected to the outlet of the expansion device 97 to function as a gas-liquid separator, to perform intermediate pressure injection for returning the gas refrigerant separated from the liquid in the receiver 18 to the second-stage compression element 202d through the second second-stage injection tube 18c (i.e., using
(13) Modification 11
In Modifications 7 through 10 described above, the configuration may be designed having a plurality of usage-side heat exchangers 6 connected in parallel to each other, the objective being to perform air cooling or air warming according to the air-conditioning load of a plurality of air-conditioned spaces, for example.
For example, the refrigerant circuits 810 and 910 in Modifications 9 and 10 described above (see
The same operational effects as those of Modifications 9 and 10 and the like described above can also be obtained with the configuration of the present modification.
(14) Modification 12
In Modifications 7 through 11 described above, a subcooler may be provided, the objective being to cool the refrigerant fed to the usage-side heat exchanger 6 and the heat source-side heat exchanger 4 so that the refrigerant reaches a subcooled state.
For example, the refrigerant circuit 1010 in Modification 11 described above (see
The subcooling heat exchanger 96 is a heat exchanger for cooling refrigerant fed from the receiver 18 through the plurality (two in this case) of usage-side expansion mechanisms 5c to the usage-side heat exchangers 6 during the air-cooling operation, and also for cooling refrigerant fed from the receiver 18 through the first expansion mechanism 5a and the intermediate heat exchanger return valve 94b to the heat source-side heat exchanger 4 and the intermediate heat exchanger 7 during the air-warming operation. More specifically, the subcooling heat exchanger 96 is a heat exchanger for performing heat exchange with the refrigerant flowing through the third intake return tube 95 which returns from the receiver 18 to the intake side of the compression mechanism 2 (i.e., to the intake tube 2a). The third intake return tube 95 is provided with a third intake return valve 95a whose opening degree can be controlled, and during the air-cooling operation in the subcooling heat exchanger 96, heat exchange is performed between the refrigerant fed from the receiver 18 to the usage-side expansion mechanisms 5c and the refrigerant flowing through the third intake return tube 95 after being depressurized to a nearly low pressure in the third intake return valve 95a, and heat exchange is also performed between the refrigerant fed from the receiver 18 to the first expansion mechanism 5a and the intermediate heat exchanger return valve 94b and the refrigerant flowing through the third intake return tube 95 after being depressurized to a nearly low pressure in the third intake return valve 95a. The third intake return valve 95a is an electrically driven expansion valve in the present modification. The third intake return tube 95 and the first intake return tube 18f are integrated in the portion near the receiver 18.
The same operational effects as those of Modification 11 and the like described above can also be obtained with the configuration of the present modification. Moreover, in the configuration of the present modification, the refrigerant fed from the receiver 18 to the usage-side expansion mechanisms 5c can be brought to a subcooled state during the air-cooling operation, and the refrigerant fed from the receiver 18 to the first expansion mechanism 5a and the intermediate heat exchanger return valve 94b can be brought to a subcooled state during the air-warming operation (in other words, using
(15) Modification 13
In the above-described embodiment and the modifications thereof, two-stage compression-type compression mechanisms 2, 102, 202 are used, but three-stage compression systems or compression mechanisms having even more stages may also be used.
For example, in the refrigerant circuit 1010 in Modification 11 described above (see
The configuration of the present modification differs from that of the above-described Modification 11, for example, in that since the three-stage compression-type compression mechanism 302 is used, the intermediate heat exchangers 7, 307 can be made to function as coolers of the intermediate-pressure refrigerant in the refrigeration cycle (the refrigerant fed to the second-stage compression element 302d after being discharged from the first-stage compression element 302c, and the refrigerant fed to the second-stage compression element 302e after being discharged from the first-stage compression element 303c) by switching the intermediate heat exchanger switching valves 93, 393 to the refrigerant non-return state during the air-cooling operation, and the intermediate heat exchangers 7, 307 can be made to function as evaporators of the low-pressure refrigerant in the refrigeration cycle (the refrigerant whose heat is radiated in the usage-side heat exchangers 6) by switching the intermediate heat exchanger switching valves 93, 393 to the refrigerant return state during the air-warming operation. However, aside from this difference, it is possible to obtain the same operational effects as those of the above-described Modification 11, for example.
(16) Other Embodiments
Embodiments of the present invention and modifications thereof are described above with reference to the drawings, but the specific configuration is not limited to these embodiments or their modifications, and can be changed within a range that does not deviate from the scope of the invention.
For example, in the above-described embodiment and modifications thereof, the present invention may be applied to a “chiller-type” air-conditioning apparatus in which water or brine is used as a heating source or cooling source for conducting heat exchange with the refrigerant flowing through the usage-side heat exchanger 6, and a secondary heat exchanger is provided for conducting heat exchange between indoor air and the water or brine that has undergone heat exchange in the usage-side heat exchanger 6.
The present invention can also be applied to other types of refrigeration apparatuses besides the above-described chiller-type air-conditioning apparatus, as long as the apparatus performs a multistage compression refrigeration cycle using a refrigerant that operates in a supercritical range as its refrigerant.
The refrigerant that operates in a supercritical range is not limited to carbon dioxide; ethylene, ethane, nitric oxide, and other gases may also be used.
If the present invention is used, high operation efficiency is obtained in a refrigeration apparatus which has a refrigerant circuit configured to be capable of switching between a cooling operation and a heating operation and which performs a multistage compression-type refrigeration cycle.
Number | Date | Country | Kind |
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2008-048904 | Feb 2008 | JP | national |
2008-322497 | Dec 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/053347 | 2/25/2009 | WO | 00 | 8/24/2010 |